I finally managed to make it work, but it is buggy, and I am wondering why it is impossible to make it save those settings as I had to change that from the database, and those settings below work OK, but never save from the browser

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When having fetched email set to archive and specify the folder, those settings are never saved and I get a blank page.
Also I noticed that there are a lot of settings that don't get deleted in ost_config and ost_email_account.